Make obsolete status exportable

[pikatech]

To make the 'obsolete' status of ontology classes exportable, some changes have to be applied.
The following changes have been applied to v1.7.1 and should also find their way into v1.8.0.

1. de.julielab.neo4j.plugins.constants.semedico.ConceptConstants.java needs a field
   public static final String PROP_OBSOLETE = "obsolete";

2. de.julielab.neo4j.plugins.datarepresentation.ImportConcept needs a new constructor to deal with the new field

public ImportConcept(String preferredName, List<String> synonyms, List<String> descriptions,
		ConceptCoordinates coordinates, List<ConceptCoordinates> parentCoordinates, Boolean obsolete) {
	this(preferredName, synonyms, descriptions, coordinates);
	this.parentCoordinates = parentCoordinates;
	this.obsolete = obsolete;
}

and a corresponding variable

@SerializedName(ConceptConstants.PROP_OBSOLETE)
public Boolean obsolete;